Radio receiving system



Jan. 13, 1931. F. P. BENJAMIN 1,788,975

' RADIO RECEIVING. SYSTEM Filed May 23, 192? IX 1? I filly illITIllllll" a! gwue'nkyp FPBENJHM/N Patented Jan. 13, 1931 tem describedand claimed in myv copending f applicationSerial No. 75,425, filed December I 514th, 1925.

RED P. BE MI warren ILLINOIS RADIQ RECEIVING SYSTEM Application filed May 23,

This invention relates to radio receiving systems and is an lmprovementover the sys- In my copending ferred to I have shown: and describeda-systerm which is an-improvementover.the usual receiving sets in that it minimizes the usual n) howls, squeals and whistles often causedby the generation of eddy currents and harmon ice. The improved results are 7 obtained without introducing lossesand without the use of any neutralizing-ibalancing.or bridg- 1-5 ing action or the like. In accomplishing-the decreasing thetran'smissionot plate voltages j desired results, the eificiencyof the'action of the grids of the electron discharge tubes is greatly increasedby providing a freer flow of current thereto.

tion provides a system which embodies the advantages of the system shown in mycopending application, and also provides the additional advantage of. minimizing the transmission of plate current to the grids,

and consequently minimizes ,the consumption from the B battery or other source em ployed. An importantxobject of the inven-' tion therefore is to accomplish the resultsobin my copending application and'to further increase the accuracy of signal reception by to the grids of .the tubes. v

cuit, through a common transformer, with;

lessened capacity effect between the two leads. 'A further object is to provide-a double A further object or theinvention' is to render practicable adoublegrid-filament cirs grid-filament circuitto permit the various 7 electric currents passing 7 through such circuits to find the. route nostsuitable' for its function.

Other objects and advantages ofthe in-,.

vention will become apparent during the course of the followingdescription.

In the drawing -I-have.shown one embodi- I ment of the invention. In this showing the single figure of the drawing is a diagram matic'view wherein for the purposeof illuse,

application above re- It has been found that the present inven tainedby the systemillustrated anddescribed 1927. Serial No. 193,688.

tration the invention is shown as applied to asingleistage of-tuned radio frequency. Referringto the drawings .the numeral 10 designates the usual antennaj lOgconnected by a lead 11 to oneendof acoil 12' ofathe usual type; The other end oft-his coiL-is;

- connected by a lead 13 ton. suitable ground 14, as shown, 'The coil i2 constitutes the primary of .a radio frequency transformer,

which includes a pair of secondary coils v 15 andld; The-coil 15 preferably includes substantially the same number of turns as the primary 12,. while the coil 16 includes a greater number of turns, depending upon the wave band tobe covered. l

The numeral 17 designatesan ordinary electron discharge tube provided with a plate 18, grid 19-and filament 20, the latterbeing provided withpositive andnegative leads;21

negative side of which is connected to the lead 23 asshown. The positive terminal of the A batteryis connected to the negative ,ter-, minal of a-B battery 32-by-a =wire 33, in the usual manner; Alead wire 34; is connected atone 91 d tothe connectingwire 33 and is adapted to supply current to the positive side of the filament through a suitable rheoe stat 35 :Oneside of the smaller secondary 15 is connected to the wire 34 by alead wire36," While the opposite end of the coil 15-; is connected to the grid lead 25 by a wire;.3 7,.a

resistance. 38 being arranged in the lead '87 for -apurpose to be described. 7

The radio. frequency stage illustrated is in the usual manner. 7 As shown, the positive side of the B battery is connectedto one end of a wire 39, and the opposite end oft-his Wire is eona et d reend t1atrant 1nr ad'aptedto be coupled to a succeedingstage V V primary coil 40. The opposite end of the coil 40 is connected to the plate 18 by a lead wire 41. It will be apparent that the coils 12, 15 and 16 are arranged in inductive relation and that the coil 40 may be arranged in a similar relation to a succeeding stage of radio frequency, or a detector, the succeeding stages rents and greatly improving the quality of reception. The function of the capacity 27 is to prevent B battery current from passing through this coil and impressing itself upon the grid. Since returns are made to each I filament lead, this capacity also'prevents a short circuit across the A battery. The function of the resistance 38 inserted'in the other grid-filament circuit is to limit the amount of B battery current that mayreach the grid through any tendency to complete its circuit by crossing between the grid and plate and also to decrease the capacity effect between the two secondaries of the trans formers. It is believed that the total elimination of grid leakages through one of the grid circuits has a strong influence on the satisfactory results obtained from the use of the circuit. The resistance referred to also tends to decrease if not eliminate any necessity for tuning the coil to which it is connected and further permits the number of turns in this coil to be'decreased in number to that employed in the usual primary coil, or even less, allowing the common transformer to be constructed with great simplicity and without undue capacity effect between the coils. WVhile the insertion of the capacity 27 inthe tuned grid circuit somewhat impairs grid action, the other grid circuit through the coil 15 acting in conjunction with the'tuned circuit, overcomes the defect referred to and provides a greatly improved grid action with completeness and accuracy of tone much superior to that of the'usual single grid-filament circuit.

The action of the resistance 38 is unique in that within the limits of practical values, such as 1/20 megohm to 20 megohms, volume increases as the resistance is increased, having the opposite effect of resistances 'in'general probably due to the fact that it serves to limit the amount of plate current traveling in an opposite direction to the currents normally in the grid-filament circuit. Increased resist-' ance therefore 1s des1rable,'and-it also is desirable for the reason that a decreasein resi st' ance might tend to detune the transformer.

The resistance 38 also provides a circuit better adapted to audio frequency currents, and handles with less confusion the detection which takes place to a greater or less extent in any radio frequency circuit.

The combination of the tuned grid circuit,

including the capacity, with the other gridcircuit, including a high resistance, retains the benefits of both, and yet provides an interaction which oifsets the disadvantages of either thus permitting reproduction of sound with greater faithfulness and with less tendency toward oscillation than in the usual grid return circuit. The return through what i might be termed the auxiliary circuit, that is,

the circuit through the coil 15 tothe positive side of the filament has the additional feature of lessening the tendency of plate current to pass to the grid through the A battery in common with thefilament circuit; as well as through the negative side of the filament, and

in multiple tube receiving systems, it lessens the tendency of feed-back affecting the action of the previous tube, reducing still further the tendency toward oscillation. Some gain in clearness also results fromithe provision of leads from the grid-to opposite sides of the filament.

The circuit illustrated shows what might be termed the main grid circuit, that is, the circuit through the coil 16, tuned by a variable capacity, but the invention is applicable to any other method of tuning, such as by a variometer or vario-coupler. The invention is readily applicable to detector,radio frequency and audio frequency circuits, and thus obviously may be applied to one tube of a multitube circuit or to all of the tubes thereof.

The words main? and auxiliary are employed merely for the purpose of description, and as a matter of fact the circuit operating most strongly will depend upon the respective values of resistance and capacity employed.

The circuit illustrated is to be considered only as one embodiment of the invention, and it is to be understood that the connections of the leads from the secondaries of the transformer to the filament of the tube may be 5 varied. In other-words, the particular con nections illustrated are not vital to the proper operation of the circuit. For instance, the" cuits. The capacity of the variable condenser 28, and the number of turns of wire employed in maklng the transformers w ll depend, of course, upon therange of frequencies which it is desired to receive. As previously stated, the resistance 38 1s not critlcal, but 1t is de-.

sired to employ a fairly high resistance with in the range outlined above. It also has been found that the capacity 27also not par in y,

ticularly critical. The several coils of the filament,

cathode and grid therein, and a pair of leads each including a transformer secondary coil inductively associated with the input circuit, said leads being connected between the grid and cathode of the tube, each of said leads including means tending to prevent the flow of direct current therethrough.

2.In a radio receiving system, an input circuit, an electron discharge tube having a cathode and grid therein, a pair of leads each including a transformer secondary coil inductively associated with said input circuit, said leads having a common connection at one end with thegrid of the tube, the opposite ends of said leads being connected to the cathode of the tube, a capacity arranged in one of said leads, and a resistance arranged in the other of said leads.

8. In a radio receiving system, an input circuit, an electron discharge tube having a filament and grid therein, a pair of leads having a common connection at one end with the grid of the tube, the opposite ends of saidleads being connected respectively with opposite ends of the tube filament, a capacity connected in one of said leads,

and a resistance, connected in the other of said leads, each of said leads including a coil winding inductively associated with said innection at one end to the grid of the tube,

each of saidsecondary coils forming a portion of one of said leads, the opposite ends of said leads being connected to the cathode of the tube, a capacity arranged in one of said leads, and a resistance arranged in the other of said leads.

5. In a radio receiving system including an electron discharge tube having a filament and grid therein, and a primary transformer 0011, a pair of secondary coils arranged ininductive relation to said primary transformer 0011, a palr of leads having a coma fixed capacity arranged in theother lead; 6. In a radio receiving system including an electron discharge tube having a filament and grid therein, and a primary transformer coil, a pair of secondary transformer coils inductively associated with said primary coil, one of said secondary coils including a suitable number of turns to cover the dea variable capacity connected 1 across one of said secondary coils, a recv sistance arranged in one of said leads, and

sired broadcast band, the other of said secondary coils including anumber of turns insufiicient for tuning, a pair of leads having a common connection at one end to the grid of the tube, each of said secondarycoils forming a part of one of said leads, the opposite ends of said leads being connected re-' spectively to the opposite ends of the tube filament, a variable capacity connected across said first mentioned secondary coil, a

capacity arranged in one of said leads, and

a resistance arranged in the other of. said leads. V i V 7. In a radio receiving system including an electron discharge tube having therein a grid, and a filament provided with positive I and negative terminals, and a primary transformer coil, a pair of leads having a common connection at one end with the grid of the tube, the opposite end of one of said leads being connected to the positive terminalof the filament, the opposite end of the other of said. leads being connected to the negative terminal of the filament, a secondary transformer coil arranged in said first mentioned lead and including an insuilicient number of turns for tuning, a secondary coil arranged in said second mentioned lead and-including a suflicient number of turns to be tuned to cover the desired broadcast band, a variable capacity connected 7 I sistance arranged in said first mentioned lead, and a capacity arranged in said second named lead. I v

Intestimony whereof I aflix my signature.

* FRED P. BENJAMIN.

mon connection at one end with the grid of the tube, each of said secondarycoils forming a part of one of said leads, the opposite ends of said leads being connected re-V spectively to the opposite ends of the tube; I

cross said last named secondary coil, a re- 7 

